菜鸡写线段树又挂了，求助WA#2 9pts

#include<bits/stdc++.h>
using namespace std;
const int maxn=5e5+10;
typedef long long int ll;
struct node
{
    ll l,r;
    ll mal,mar;
    ll sum;
    ll ans;
}c[maxn<<2];
ll a[maxn];
void pushup(int x)
{
    c[x].mal=max(c[x<<1].mal,c[x<<1].sum+c[x<<1|1].mal);
    c[x].mar=max(c[x<<1|1].mar,c[x<<1|1].sum+c[x<<1].mar);
    c[x].sum=c[x<<1].sum+c[x<<1|1].sum;
    c[x].ans=max(max(c[x<<1].ans,c[x<<1|1].ans),c[x<<1].mar+c[x<<1|1].mal);
}
void build(int l,int r,int x)
{
    if(l==r)
    {
        c[x].l=l,c[x].r=r;
        c[x].mal=c[x].mar=c[x].ans=a[l]=c[x].sum=a[l];
        return;
    }
    c[x].l=l;c[x].r=r;
    int mid=(l+r)>>1;
    build(l,mid,x<<1);
    build(mid+1,r,x<<1|1);
    pushup(x);
    return;
}
void modify(int x,int pos,int k)
{

    if(c[x].l==c[x].r)
    {
        c[x].sum=c[x].mal=c[x].mar=c[x].ans=k;
        return;
    }
    ll mid=(c[x].l+c[x].r)>>1;
    if(mid>=pos)
        modify(x<<1,pos,k);
    else
        modify(x<<1|1,pos,k);
    pushup(x);
    return;
}
node query(int x,int l,int r)
{
    if(c[x].l>=l&&c[x].r<=r)
        return c[x];
    ll mid=(c[x].l+c[x].r)>>1;
    if(mid>=l)
        return query(x<<1,l,r);
    else if(mid+1<=r)
        return query(x<<1|1,l,r);
    node ls=query(x<<1,l,r),rs=query(x<<1|1,l,r),ans;
    ans.l=c[x].l;ans.r=c[x].r;
    ans.mal=max(ls.mal,ls.sum+rs.mal);
    ans.mar=max(rs.mar,rs.sum+ls.mar);
    ans.sum=ls.sum+rs.sum;
    ans.ans=max(max(ls.ans,rs.ans),ls.mar+rs.mal);
    return ans;
}
int main()
{
//  freopen("P4513_2.in","r",stdin);
//  freopen("P4513.out","w",stdout); 
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
    }
    build(1,n,1);
    for(int i=1;i<=m;i++)
    {
        int op,x,y;
        scanf("%d",&op);
        if(op==2)
        {
            scanf("%d%d",&x,&y);
            modify(1,x,y);
        }
        else
        {
            scanf("%d%d",&x,&y);
            printf("%lld\n",query(1,min(x,y),max(x,y)).ans);
        }
    }
    return 0;
}